Many forms of generator have been used in the United States for the production of water gas, which, after or during manufacture, is mixed with the vapors and permanent gases obtained by cracking various grades of paraffin oil, and “fixing” them by subjecting them to a high temperature; and in considering the subject of enrichment of coal gas by carbureted water gas, I shall be forced, by the limited time at my disposal, to confine myself to the most successful of these processes, or those which are already undergoing trial in this country.

In considering these methods, we find they can be divided into two classes: 

1.  Continuous processes, in which the heat necessary to bring about the interaction of the carbon and steam is obtained by performing the operation in retorts externally heated in a furnace; and

2.  Intermittent processes, in which carbon is first heated to incandescence by an air blast, and then, the air blast being cut off, superheated steam is blown in until the temperature is reduced to a point at which the carbon begins to fail in its action, when the air is again admitted to bring the fuel up to the required temperature, the process consisting of alternate formation of producer gas with rise of temperature, and of water gas with lowering of the temperature.

Of the first class of generator, none, as far as I know, have as yet been practically successful, the nearest approach to this system being the “Meeze,” in which fire clay retorts in an ordinary setting are employed.  In the center of each retort is a pipe leading nearly to the rear end of the retort, and containing baffle plates.  Through this a jet of superheated steam and hydrocarbon vapor is injected, and the mixture passes the length of the inner tube, and then back through the retort itself—­which is also fitted with baffle plates—­to the front of the retort, whence the fixed gases escape by the stand pipe to the hydraulic main, and the rich gas thus formed is used either to enrich coal gas or is mixed with water gas made in a separate generator.  In some forms the water gas is passed with the oil through the retort.  In such a process, the complete breaking down of some of the heavy hydrocarbons takes place, and the superheated steam, acting on the carbon so liberated, forms water gas which bears the lower hydrocarbons formed with it; but inasmuch as oil is not an economical source of carbon for the production of water gas, this would probably make the cost of production higher than necessary.  This system has been extensively tried, and indeed used to a certain extent, but the results have not been altogether satisfactory, one of the troubles which have had to be contended with being choking of the retorts.